1. Field of the Invention
This invention relates generally to a means and method for reducing vibration in hard-disk drives and more particularly to apparatus, systems, and methods for reducing off-track vibration in disk drives having asymmetrical integrated lead suspensions.
2. Description of the Related Art
A typical hard-disk drive will include a stack of disks or “platters” mounted on a common spindle. The surfaces of the disks are typically coated with a material that is readily magnetized and demagnetized. A number of read/write heads may be positioned over the disks as the disks are spun to magnetize portions of the disks to write information thereon or detect the magnetized portions to read information therefrom. A plurality of read/write heads may be used to simultaneously read information from multiple rigid platters that are typically arranged in a vertical stack and rotated as a unit via the spindle.
Information may be stored in concentric circles or tracks on the surface of the disks. Thus, to access information stored on the hard drive, the read/write head must first be moved radially to the correct track where the information is stored. The greater the number of tracks, the greater the amount of data that may be stored on the hard-disk drive. However, increasing the density of the tracks decreases the distance between tracks. Therefore, in order to accommodate greater track densities it is important that a read/write head be positioned as accurately as possible in order to read data from, or write data to, the correct track. Aberrant motion caused by vibrations and other effects may interfere with precise positioning and must therefore be avoided.
The read/write heads are typically moved from one track to another by an actuator that is capable of very precise movements. A suspension may be interposed between the read/write heads and the actuator in order to provide a degree of flexibility, enabling the read/write heads to “float” on the surface of the disk on a very thin layer of air, or “air bearing,” as the disks spin at a very high speed relative to the read/write heads. The combination of suspension and read/write head is often referred to as the head-gimbal assembly (HGA).
The suspension may include a load beam, a mount plate, a hinge plate and a flexure. The suspension secures to an arm through the mount plate, or another similar member. The arm is typically rotated by a voice coil, or other actuating mechanism. The hinge plate secures to the mount plate and flexibly secures the load beam and flexure to the arm. The load beam is typically substantially rigid and extends a substantial distance over the disks. The vertical flexibility and gram load of a suspension are provided by the hinge plate. The flexure is typically flexible in the pitch and roll directions and together with the gram load of the hinge plate is primarily responsible for enabling flotation of the read/write heads.
Electrically conductive traces extend from the read/write head and along the flexure, mount plate, and load beam, in order to transport electrical signals from the read/write head to and from drive electronics. The drive electronics interpret signals from the read/write head in order to retrieve data or send the appropriate signals to the read/write head causing it to write information to the disks. In some hard-disk drive suspensions, the traces are integrated with the suspension in order to provide ease of manufacture and high data rate capability. Such suspensions are referred to as integrated lead suspensions (ILS).
A typical ILS has traces routed from the read/write head symmetrically along the centerline of the suspension until just ahead of the hinge plate. At this location the traces typically make a 90 degree turn and go along the lateral side of the load beam, hinge plate, and mount plate. This asymmetric routing of the traces on one side of the suspension can create off track motion of the read/write head at certain frequencies and conditions.
In a typical hard disk drive a read/write head and flexure is provided for each data-bearing surface of each disk. The suspensions are swaged onto arms which interleave with the platter stack creating a “comb” shaped structure. Arms corresponding to disks in the middle of the stack may have two suspension and read/write head assemblies secured thereto in order to read from the disks above and below. However, the arm corresponding to the uppermost and lowermost disk typically include only a single suspension and read/write head either because the top surface of the uppermost disk and the bottom surface of the lowermost disk are usually not used to store data or because there is no other disk below or above the uppermost and lowermost disks providing a data-bearing surface requiring a read/write head.
Experiments conducted by the inventor indicate that the asymmetric routing of the traces on integrated lead suspensions typically does not cause deleterious vibration of the HGAs corresponding to the middle disks, inasmuch as each arm has two suspensions and read/write head assemblies secured thereto, which are typically mirror images of one another. Experiments conducted by the inventor indicate that although the HGAs of the middle disks do have vibration modes caused by the asymmetrical traces, the vibration modes are out of phase with one another and cancel each other out. As previously stated, the uppermost and lowermost arms each have a single suspension and read/write head assembly secured thereto. Experiments conducted by the inventor indicate that for the uppermost and lowermost arms the harmful vibration modes are not cancelled out and high magnitude off-track vibrations can occur.
Prior attempts to correct vibration in outer HGAs have used dummy members mirroring only the inertial properties of the flexure and read/write head assembly. None have provided a means for compensating for the dynamic interaction of the traces with the other components of the HGA.
In view of the foregoing, it is apparent that a need exists for an apparatus, method, and system for compensating for off-track vibration modes caused by asymmetric routing of traces in integrated lead suspension (ILS) head-gimbal assemblies (HGAs). Such an apparatus should be easily manufacturable. To that end, it would be an improvement in the art to provide an apparatus that is a single member easily securable to an actuator arm.